telecom Flashcards
what are the transmission mode
- Broadcasting which involves the use of a single powerful transmitter and
numerous receivers that are relatively inexpensive to build; example: radio and
television. - Point-to-point communication in which the communication process takes place
over a link between a single transmitter and receiver. In this case, there is usually a
bidirectional flow of information signals which requires the use of a transmitter
and a receiver at each end of the link; example: telephone and a link between an
earth station and a robot navigation the surface of another planet.
what are the transmission moes
- Simplex: information is sent in one direction. Examples are Radio or TV
broadcasting. - Half duplex: information is sent and received on the same channel but not at the
same time. Examples are: Walky Talky, Bluetooth data transfer between two
laptops, etc… - Full duplex: information is sent and received at the same time over two separate
channels. The telephone is an example of full duplex communication.
why do we use digital communications
easy to regenerate distorted signals
easier and more efficient to multiplex several signals
can combine difference signal types
what are the transmission
mediums
guided:
twisted pair, coaxial cable, fiber optic
UTP cable, stp cablecable
unguided
radio waves, microwaves
what is the difference between coaxial and STP
STP uses a foil shield while while coaxial uses a plastic insulation
what are the components of a fiber optic cable
jacket
strengening material
buffer
cladding
core
what are the types of fiber optic cables
single mode
used for long distances
4-5 times more expensive than multimode
core has a smaller radius
uses a lazer as a light source
handling or manufacturing is much harder
less degradation of signals
can carry singals at much greater speed
multimode
what is a PSTN
the public switched telephone network is an overall telecom network consisting of local networks interconnected by one or more long distance networks
what are the satellite services
fixed satellite services (FSS)
broadcast satellite services (BSS)
Mobile satellite service (MSS)
Inter Satellite service (ISS)
what is a molniya orbit
highly or extremely eliptical orbit
what are the 3 segments of a GPS system
Space segment (ss)
control segment (CS)
User segment (US)
what are the 3 entities of a control segment
Master control system
monitor stations
ground antennas
what do antenna noise
temperature Td depend on?
loss between the antenna and receiver input
sky noise from the galaxy, sun and moon
absorption by amospheric gases and precipitation
radiation from the earth into the backlobes of the antenna
interference from man made radio sources
how do you get rid of antenna noise
by placing a metallic rim around the edge of the parabolic dish
what are the atmospheric effects on microwaves
absorption
refraction
diffraction
what is a microwave link
A (terrestrial) microwave link uses a beam of radio waves in the
microwave frequency range to transmit information between two fixed
locations on the earth.
what is frequency reuse
in the context of polarization, same frequency channels can be reused by passing one horizontal and one vertical signal through it
what are the two types of towers and when is each one used
self supporting : relatively short towers
guyed towers: for relatively long towers or when there is no space at the base
what is refraction
refraction is the bending of the radio waves due to changes in the atmosphere (temperature/density/altitude)
describe the condition with respect to n1, n2, and k
if n1 > n2 => Good Condition
if n2 > n1 => Bad condition
if K < 0 => Good Condition
if 1 < k < 0 => Bad Condition
if k > 0 => Good conidtion
if k -> inf => Good condition
what is ducting
atmospheric refraction sometimes traps microwave beams in a waveguide called ducting
what are the components of a setellite
command antenna
broadcast antenna
radio transmitters and receivers
rocket fuel
rocket thrusters
main rocket
camera
solar panels
what is a FSS
a fixed satellite station supports telecommunication services between antennas (satellite and ground station)
what is a BSS
a broadcast satellite station uses a high powered beam to transmit radio or television services right to the end user (Simplex)
